PKODDCTS DERIVED FROM TURPENTINES, 229 



ing. All the liquefied material which reaches above o, runs out 

 into the receptacle r, so that there remains behind in the boiler 

 only a small quantity of resin mixed with foreign matters, such as , 

 chips of wood and bark, leaves, sand, &c. The filtered resin is 

 transferred from »• to a reservoir ch, called the charge, holding the 

 exact quantity (about 66 gallons) for each operation. From this 

 reservoir the resin is introduced into the still st. In the still a 

 perforated worm permits of the introduction of steam when the 

 resin, heated by the fire at /, has attained a temperature of 135°. 

 Effervescence ensues and the oil separates completely ifrom the 

 colophony, passing over, with the steam, into the serpentine con- 

 denser, whence it falls into the tub t. The tub is furnished with 

 two taps, by means of which the oil and water are drawn ofi" sepa- 

 rately. At the bottom of the still is an opening op, which is closed 

 with a bung and carefully luted. When the oil ceases to pass 

 into the condenser, the distilling operation is stopped and the 

 bung removed. The colophony, at a temperature of about 130°, 

 escapes into a box ho, and thence into a revolving cylinder ni 

 formed of very fine metallic gauze. The colophony falls throuo-h 

 into a receptacle, while an unimportant residue is left inside. The oil 

 on passing out, is cloudy, but after standing for four to five days in 

 large earthenware jars or copper pots, clears up, the small quantity 

 of impurities present becoming precipitated. To prevent the solid 

 matters in the resin from burning, the boiler b may be fitted with 

 an agitator. Moreover, steam alone may be employed throughout 

 the operation, thus avoiding all risk of burning. 



There are different grades or qualities of colophony. The first 

 exudations from new or recently freshened bJazes give the best 

 kinds, while the hard or semi-hardened concretions (thus, scrape 

 in French, galipot and barras, the latter being the scrapings con- 

 taining debris of wood and bark) yield an inferior yellow resin. 

 The lowest class is furnished by the distillation of the filtration 

 residues left in the manufacture of the better kinds. If, while 

 the rosin is still liquid, some water is added and the whole is briskly 

 agitated, opaque rosin is obtained owing to the formation of abietic 

 acid. 



The pitches are produced either by a further distillation of the 

 tar obtained in the dry distillation of highly resinous wood or by 

 the distillation of the filtration residues left in the various processes 

 followed for separating the oil from the colophony. In the more 

 primitive of these processes the filtration of the crude resin and 

 colophony is effected through mats. The mats, with what is left 



